β-α Photoisomerization of Cobaloxime Complexes in the Solid State. III. Accelerated Reaction Rate by Hydrogen Bond

The crystal structures of two cobaloxime complexes with different axial base ligands have been determined by X-ray analysis at room temperature. I: (3-Aminopyridine)(2-cyanoethyl)bis(dimethylglyoximato)cobalt(III); the cystal is monoclinic, the space group being C2⁄c, Z=8 with a=28.849(8), b=7.746(2), c=18.429(5) Å, and β=105.71(3)°. II: (Aniline)(2-cyanoethyl)bis(dimethylglyoximato)cobalt(III) aniline solvate; the crystal is monoclinic, the space group being P21⁄c, Z=4 with a=14.228(7), b=11.426(4), c=14.178(3) Å, and β=91.92(3)°. Both structures were refined by a full-matrix least-squares method to final R values of 0.070 and 0.074 for 3886 and 3311 observed reflections, respectively. Their photoisomerization rates in the solid state obtained from changes in the IR spectra, 3.2 and 4.2×10−4 s−1, respectively, are significantly greater than those of the related compounds. The hydrogen bonds between the reactive 2-cyanoethyl groups and the atoms of the neighboring molecules in the two crystals should be responsible for the greater reaction rates. Taking into account the role of the hydrogen bonds, a probable isomerization mechanism is proposed.